Many Changes to Client

1. Rename the client package to 'server'
2. Delete the existing client-cli. I don't think the code is gone yet, but it's all commented out. We're getting rid of the cli altogether and instead using 'termbox'. The new termbox frontend has not been built yet.
3. Added a cli interface to running the server, using the library 'cobra'.
4. Added a bunch of configurable options to running the server, leaving room for a config file reader/manager. That's not in this PR, but it's coming soon. (after wallet facelift)
5. Switched all of the server commands to using RPC, with the exception of the wallet stuff becuase that's getting a facelift anyway. The wallet facelift will be the next PR.

Unfortunately Sia's back to being unusable as of this PR, because we need to get the termbox stuff working (after config file PR). Hopefully all of this will be done by the end of the week.
I dunno. What if you can't find the home directory, but a config file is specified anyway? Then it really doesn't matter.

I think that this library is the wrong place to panic. Either you find a home file or you don't, and it's up to the lower layers to decide what to do with that problem. They could potentially create the home dir if one is not found (which is what most applications do anyway).